Power take-off devices are well known in the heavy-duty, commercial and industrial truck and equipment industries. Power take-off (PTO) devices are used to run various pieces of auxiliary and accessory equipment that maybe attached to such vehicles and equipment, and/or the vehicle and equipment themselves. Typically, the engine associated with the vehicle is used to drive the vehicle and/or the auxiliary equipment when the PTO is enabled and engaged.
One example of a specific use of PTO devices is with refuse collection vehicles. When the PTO is engaged, the operator of the vehicle can compact loose refuse placed therein using the PTO device, which uses engine power to operate a compacting device. Another specific example of the use of PTO devices is with concrete delivery vehicles. The PTO uses the power from the engine to operate the mixing drum as the vehicle transports the concrete to the job site and further to dispense the concrete upon reaching the job site. In either case, the engine used to drive the PTO device may additionally or alternatively be used to drive the vehicle itself. Many other types of vehicles and equipment use PTO devices as well, such as dump trucks, agricultural tractors and construction equipment, to name a few. PTO devices may be used to provide power to such items as pumps, lifts, blowers, and other mechanisms known to those in the commercial and heavy-duty equipment industries.
Typically, the engine speed regulates the speed of the PTO operation while the PTO is engaged. As one specific example of such a system, a pair of operator switches may be used to control PTO operation: 1) a first switch, typically an ON/OFF switch, is used to enable and disable PTO operation; and 2) a second switch, typically a "SET/RESUME" switch, is operable in the SET position to set PTO speed to a first engine speed, and in the RESUME position to set PTO speed to a second engine speed. In PTO operations involving a moving vehicle, the PTO operation is typically limited to calibratable engine speeds, such as 1000 rpm to 1200 rpm. This is due to the operating speed limitations of many PTO devices. In vehicles having a cruise control system, the ON/OFF and SET/RESUME switches used for PTO operation are the same switches provided in known cruise control systems. However, many engines/vehicles operable to drive one or more PTO devices do not include cruise control systems therein, and in the general case the ON/OFF and SET/RESUME switches may be any operator controlled switches.
When PTO operation involves a moving vehicle, many problems may arise involving control of the vehicle speed while the PTO is engaged. For example, it is known in the art for the PTO to disengage when the operator presses a brake or vehicle clutch. U.S. Pat. No. 5,611,751 to Ehrenhardt et al. discloses a PTO control system in which vehicle speed may be controlled by the brake or clutch while the PTO remains engaged.
Another common feature of PTO systems is for the PTO to disengage upon deflection of the accelerator pedal. Alternatively, the engine may be unresponsive to manual manipulation of the accelerator pedal while PTO is engaged. Each of these features are designed primarily to protect the PTO device from being run or engaged at too high of a speed, i.e. in excess of the speed limitations of the PTO device. Unfortunately, these features also cause the PTO to disengage under conditions in which it would be advantageous to have accelerator pedal control of engine speed. Increased engine speeds are not always harmful to the PTO apparatus, such as increasing engine speed for only a short duration, and the PTO device is performing work below its design limitations.
PTO device operators typically bypass the above described PTO control mechanisms by manually disengaging PTO operation using the ON/OFF switch in order to accelerate the engine. However, to resume the PTO set speed, the operator is required to re-engage PTO operation when it is again needed. Thus, known PTO systems suffer the drawback that the operator is required to continuously manually manipulate the PTO ON/OFF switch in order to accelerate the engine. This activity may divert the operator's attention away from the safe operation of the vehicle/engine and other duties the operator might be required to perform.
What is needed, therefore, is a PTO control system that allows engine speed to be easily controlled by accelerator pedal activity while the PTO is engaged, i.e. a PTO control system that allows accelerator pedal over-ride of PTO operation to thereby increase engine speed, yet resumes the previously set PTO speed as the engine speed decreases thereto. The system should be reliable and simple to operate, and should be able to be readily integrated into an existing control system. Finally, the system should allow the vehicle to be operated safely in conjunction with the PTO operation.